— Shuttle astronauts could stay in space until Saturday if necessary (Image: NASA TV)
The space shuttle Atlantis will stay in space at least one extra day so that NASA can investigate the nature of two objects seen floating near the orbiter on Tuesday and because of a bad weather forecast for its landing site in Florida.
Atlantis was scheduled to come home on Wednesday morning. Now, its first landing opportunity will be no earlier than 0622 EDT (1022 GMT) on Thursday.
At 0245 EDT (0645 GMT) on Tuesday, ground controllers using a camera from the shuttle's payload bay for routine Earth observations saw an object floating beneath the orbiter. Watch a Windows Media Player movie of the mysterious debris near the shuttle.
This occurred shortly after the orbiter's reaction control system jets did a standard test firing and the flight control systems were checked out in preparation for landing.
Then, the shuttle crew reported seeing a second object floating away from Atlantis at 1200 EDT (1600 GMT).
"We're not joking about this," commander Brent Jett radioed the ground. "Dan (Burbank) was at window 1 He saw an object floating nearby. It's fairly small."
Jett estimated that it was moving at one to two feet per second (about 0.5 metres per second). Both objects are moving in the same orbit as the shuttle, so NASA managers know they have to have come off the orbiter itself.
All shook up
Shuttle programme manager Wayne Hale says he suspects the first object spotted may have shaken loose when Atlantis was testing its jets and flight control systems for landing. Previous crews have said that those tests can sound like a howitzer cannon firing.
"That's why the suspicion is that this is something that occurred around the flight control system checkout because it does shake the vehicle pretty good," Hale says.
NASA planned to inspect the payload bay with cameras on the elbow of the shuttle's robotic arm on Tuesday. They were expected to look for anything that might be missing, such as spacewalk tools or thermal blankets.
But ground controllers do not know the size, mass or distance of the first object spotted, so they were not able to figure out where it might have come from on the orbiter. "This will probably always remain a mystery as to what this was," Hale says.
The objects could be something that would not affect the safety of the shuttle, such as ice or a gap filler that came loose from the orbiter's heat shield. Or more seriously, they could be an important part of the heat shield.
NASA says it may have detected one or both of the mysterious objects shaking off the orbiter or bumping into the shuttle's wings overnight on Monday. That is because accelerometers that measure vibrations in the leading edges of the wings picked up eight possible impacts over a two-minute period on the right wing at that time. The accelerometers were added after the Columbia disaster in 2003 to measure impacts from foam insulation or ice during launch.
"Right now, I'm not taking [the vibrations] as a plus or a minus," says Hale. "It's just a piece of data."
During the day on Monday, before the accelerometers detected the vibrations, the crew used the shuttle's robotic arm and a boom extension to scan the heat shield for damage from space junk and micrometeoroids. They detected nothing amiss.
On Wednesday, Atlantis's astronauts may be asked again to use the shuttle's robotic arm to inspect the orbiter's heat shield, including the right wing, for anything that may have come off.
NASA officials say Atlantis has enough supplies to postpone its landing until Saturday if necessary.
If there is a serious problem with the heat shield, NASA has two days to decide whether they want Atlantis to redock with the International Space Station (ISS). Atlantis departed the outpost on Sunday.
That would make for cramped quarters on the ISS, which is expected to get another group of three visitors on Wednesday when a Russian Soyuz spacecraft arrives with a new crew and space tourist Anousheh Ansari.
The shuttle's astronauts could also make a spacewalk to inspect or repair any damage to the heat shield. The shuttle carries four different tools for repairing this shield. These are also a product of post-Columbia safety improvements.
"This is a mark of the new culture in space shuttle programme," Hale says. "We have not brushed this off. We're taking it very seriously."
The possibility of thunderstorms and strong winds at the landing site at Florida's Kennedy Space Center also contributed to the decision to delay landing by a day.